Injection devices are used for the convenient administration of medicaments. For example, auto injectors may be used for providing a single metered dose of a medicament, such as Epinephrine, in an emergency or for providing regular metered doses of a medicament, such as insulin. An example of one such injection device is shown in the applicant's co-pending application PCT/GB2011/051950. Such injectors typically comprise a housing within which is housed (or defined) a syringe or cartridge containing medicament. For simplicity the present application uses the term “syringe” but it will be appreciated that this is used in a non-limiting manner and is intended to encompass cartridges and/or other arrangements which may be either discrete or integral to the housing. The housing generally includes an actuation mechanism which may be of any convenient form and is arranged to move a plunger between an initial rearward, position and, a forward, delivery position so as to express medicament from the syringe.
It is known to provide such injection devices with an activation indicator which provides one or more of a visual, tactile or audible indication of the firing of the injector actuation mechanism. In particular since the delivery of a desired dose of medicament may take a certain amount of time after the user activates the injector (particularly for example, with high viscosity drugs or small needle diameters) it is useful to provide an injection complete indication. The term “Injection Complete” (or “injection completion”) is used to refer to a condition in which a satisfactory delivery of the medicament has been achieved.
It is desirable for auto injectors to be of a compact form so that they can be carried around and used unobtrusively (typically such auto injectors are provided in a pen injector type form). Further compact injectors may be simple to manufacture, assemble and use with consequent savings in manufacturing and assembly costs, and a lower environmental impact. Accordingly, any activation indicator provided within the injector must be of compact form and not significantly impact the overall size of the injection device.
Embodiments of the present invention are intended to address at least some of the abovementioned problems.